How do I check that a Java String is not all whitespaces?

To check if a Java String is not all whitespaces, you can use the trim() method to remove any leading or trailing whitespaces from the string. Then you can check if the string is empty or null. Here's an example:

String str = "    ";
if (str != null && !str.isEmpty()) {
    System.out.println("The string is not all whitespaces.");
} else {
    System.out.println("The string is all whitespaces.");
}

Alternatively, you can use the matches() method of the String class to check if the string matches the regular expression \S (which matches any non-whitespace character). Here's an example:

String str = "    ";
if (str.matches("\\S")) {
    System.out.println("The string is not all whitespaces.");
} else {
    System.out.println("The string is all whitespaces.");
}

In both cases, the output will be:

The string is not all whitespaces.